Neutralized system



Sept. 30, 1941.

I K. POSTHUMUS NEUTRALIZED SYSTEM I Filed Aug. 10, 1938 Z'SheeLs-Shest 1F/ZAMENT SUPPZ. Y MACH/NE 4 'i ru m BRI DGES ENVENTOR PGSLHUM ATTORNEYGRID SUPPZY Sept. 30, 1941. K pos umus 2,257,570

NEUTRALI ZED SYSTEM Filed Aug. 10, 1938 2 Sheets-Sheet 2 WIRE SYSTEMS Iv ,4 \H./-'. arm/ 55 GRID I F/[AMENT SUPPLY SUPPLY INVENTOR ATTORNEYPatented Sept. 30, 1941 UNITED STATES PATENToFFIcE signor, by mesneassignmentato-Radio Corporation of America, New York, N. Y., acorporation of Delaware Application August 10, 1938, Serial No. 224,063In Germany September 10, 1937 8 Claims.

This invention relates to a high frequency amplifier comprisingneutralizing condensers for.

compensating the capacity between anode and grid of the discharge tubesavailable in the arrangement.

It is sought to design the arrangement in such manner that theneutralization is independent of the frequency, since otherwise therewould be a risk of one or more spontaneously generated oscillationsoccurring in addition to the oscillations to be amplified. This resultcould always be obtained in arrangements, wherein the conductorsconnecting one or more electrodes to connecting points outside the tubehave an inductance which may be neglected for the oscillations to beamplified.

In the case of short wave amplification, however, the obtention ofsuflicient stability involves serious difficulties, since for theseshort waves the inductance of the same conductors is not negligible.This applies more particularly for amplification of large quantities ofenergy for which water-cooled tubes are usually employed since it isnecessary, in view of the size of the'tubes, to increase the length ofthe different conductors.

According to the present invention the desired effect is obtained bytuning the conductors, by which one or more electrodes are connected toconnecting points outside'the tube and whose inductance is notnegligible for the oscillations to be amplified, to the frequency of theoscillations to be amplified, and by inserting a damping resistance inthe conductor through which the input impedance and the neutralizingoondenser(s) are connected to the grid, said damping resistance beingshunted by a short circuit for the oscillations to be amplified. Thisshort-circuit preferably consistsof the series connection of aninductance and a capacity which is tuned to the frequency of theoscillations to be amplified.

' The invention will be more clearly understood byreference to theaccompanying drawings.

Figure 1 shows the diagram of connections of a well known neutralizedamplifier comprising two push-pull connected discharge tubes.

Figure 2 is the substitution diagram of the arrangement shown in Figure1.

, Figure 3 shows the same diagram of connections but embodies theimprovement according to the invention.

Figure 4 illustrates an improvement of the arrangement shown in Figure3, and

Figure 5 represents an arrangement compris-- ing an amplifying tube,according to the invention- In Figure 1, the cathode grid and anode oftwo push-pull connected discharge tubes are designated by K1, G1, A1 andK2, G2, A2 respectively. Between the grids G1 and G2 is connected anoscillatory circuit 3 to which are supplied the oscillations to beamplified and which is tuned to the frequency of the oscillations to beamplified. A circuit 4, which is also tuned to the frequency of theoscillations to be amplified, is connected between the anodes A1 and A2of the tubes l and 2. The anodes A1 and A2 are connected to the grids G2and G1 respectively through neutralizing condensers designated by C1 andC2. The cathodes K1 and K2 are interconnected through a conductor 5. Forthe sake of clearness the required feed sources are not represented inthe drawings.

When using water cooled discharge tubes in the arrangement shown inFigure 1 the plates of the neutralizing condensers connected to theanode can be provided in the immediate vicinity of the anode, so thatthe conductors connecting the anodes A1 and A2 to'the connecting points01 and 02 may be made very short so as to have a negligible inductanceto the oscillations to be amplified. However, the conductors 1connecting the grids. G1 and G2 to the connecting points P1 and P2respectively, as well as the cathode connecting leads 5 usually havesuch a length that the inductances of these leads are not negligible inamplifying ultra high frequency oscillations.

Figure 2 shows the substitution diagram of the arrangement representedin Figure 1, wherein the condensers between the point G1, K1, A1 and G2,K2, A2 respectively represent the inter-electrode capacities of thetubes I and 2 respectively. whereas the inductances 5, l, 8 representthe connecting leads between the two cathodes K1, K2 between the grid G1and the connecting point P1 and between the grid 2 and the connectingpoint P2.

When the reactances of the inductances 5, I and 8 have a negligiblysmall value the arrangement shown in Figure 2 constitutes a Wheatstonebirdge so that with a suitable size of the condensers C1 and C2 atension set up between the points A1 and A2 cannot cause a tensionbetween the points G1, K1 and G2, K2 respectively. When amplifyingfrequencies at which the reactances of the conductors and 8 are notnegligible the equilibrium of the bridge is disturbed so that thedesired neutralization is not ensured. Moreover, the conductor 5 istraversed by a current which, at these high frequencies, brings aconsiderable 5 potential difi'erence between the points K1 and K:

equal and opposite to the inductance of the coirductors. In this casethe total reactance of each I of the conductors 5, 1 and 8 will be zerofor the frequency of the oscillations tobe amplified so included in thecathode lead of the corresponding tube. Consequently, the coil 20 in thegrid supply conductor 1 of the tube l is coupled to a coil 22 insertedin the part of the conductor 5 between the point l4 and the cathode K1,whereas the coil 20 in the grid supply conductor 8 of the tube 2 iscoupled to a coil 22 inserted in the part of the conductor 5 between thepoint l4 and the cathode K2. The maximum output energy is obtained byproportioning the coupling so that the coupling between the electrodesupply conductors inside the tube is completely removed.

that complete neutralization canj'beachieved for" this frequency. Forall other frequencies,'however, ther is no equilibrium in the bridgearrangement, so that additional'measures have to be taken for avoidingthe spontaneous generation of oscillations having other frequencies,more particularly higher frequencies. According to the inventionthismeasure; consists in inserting a damping resistance intheiconductors"! and' 8 through which the input. impedance and theneutralizing. condensersare connected to the grids, said dampingresistancebeing bridged by ashortcircuit for the oscillations" to. bamplified.

Figure 3 shows a. circuit arrangement according to the invention whichsubstantially corresponds to the arrangement shown in Figure 1', butwhich embodies. the improvements constituting the obj ectsof theinvention" The conductor 1' between G1 and. P1 and conductor 8 betweenG2 and P2 include a series condenser 11 by means of which theseconductors are tuned to the frequency of the. oscillations to beamplified. Furthermore, these conductors comprise a damping resistancel9 which is bridged by ashort circuit for the oscillations. to beamplified. This short circuit consists of'the series connection of aninductance 2B and a capacity 2| which are together tuned to thefrequency of. the oscillations to be amplified. Furthermore, theconnecting line 5. between K1 and K2 comprises condensers l5 and [6 bymeans of which each of th two parts. of this connecting line on eitherside of the connecting point [4 of the circuits 3 and dare tuned to thefrequency of the oscillations to be amplified Of course, completesuppression ofany reaction, such as is ensured by the'arran-gementaccording to the. invention, causes a decrease in amplitude of theoscillations occur-ring in the circuit 4. To provide that. theamplification. is as strong as possibl it is consequently desirable inthe arrangement according to the invention toavcid all influences thatmay'invol've a further decrease of the output voltage. One of thesedetrimental influences is the mutual induction between the. conductorsthat connect the electrodes of the amplifying tubes to connecting pointsoutside the tube. In fact, this mutual induction causes a negative backcoupling between the circuits 4 and 3 thus causing a decrease of theoutput voltage.

According to. a further feature of the invention this detrimentalinfluence is entirely or partly removed by providing that theinductance, which forms part of the circuiticonstituting. for thefrequency to be amplified a short circuit of the damping resistanceincluded in th grid cir-' cuit, is inductively coupled to the cathodelead.

Figure 4 shows one form of construction of an amplifying circuitaccording totheiinvention, wherein this arrangement. is used. Each ofthe inductances is coupled. to an inductance 22 1 Figure-5- showsanamplifying arrangement according toltheinvention which differs from thearrangerrrent represented in Figure 4 in that there is provided only asingle amplifying tube I.

.The output. circuit 4 is connected between the anode and the cathode ofthe tube l and the grid is connected to one end of the input circuit 3whose other end is connected through a neutralizing condenserCi to thanode. A point. on the input circuit 3 between the ends is connected toa point M of the cathode: conductor 5. In, this arrangement theelectrode-supply conductors 5, II and I, are tuned, when necessary, bymeans of condensers l5, l8 and ll to the frequency of the, oscillationsto be amplified, and the grid con.- ductor, 1 comprises a, dampingresistance ['9 which is bridged by the series connection of a coil 20and a condenser 2| tuned to the frequency of the oscillations to beamplified. The coil 20 is inductively coupled to a coil 22 inserted inthe cathodeconductor 5.

The coils 20 and 22 shown in Figures 3, 4, and 5 need only have a slnallself induction and will often consist only of a single turn.

,Iclaim2.

g1. Inanultra-high' frequency amplifying system, an electron dischargetube having an input electrode, a cathode and an output electrode, ahighfrequency' input circuit, a high frequency output circuit, meansseries tuned to the frequency of said input circuit connecting saidinput circuit to said input electrode, a damping resistance inseries-With said means, means connecting said output circuit to saidoutput electrode, neutralizing'means coupling said input and outputelectrodes, and a circuit series tuned to the frequencyof operation ofsaid high frequency input circuit connecting said cathode to said high.frequency circuits.

2'. In an ultra high frequency amplifying system, an electron dischargetube having an input electrode, a cathode and an output electrode, ahigh frequency input circuit, a high frequency output circuit, meansseries tuned to the frequency of said input circuit connecting saidinput circuit to said input electrode, means connecting said outputcircuit to said output electrode, neutralizing means coupling said inputand output electrodes, a circuit series tuned to the frequency ofoperation of said high frequency circuits connecting said cathode tosaid high frequency circuits and a coupling between said series tunedcircuit and said means series tuned to the frequency of said inputcircuit.

3. In a neutralized-amplifier comprising an electron discharge devicehaving input and output electrodes including a cathode, high frequencyinput and output circuits connected with the input and output electrodesin said device respectively and aneutralizing circuit inter-connectingthe said input and output electrodes, means for stabilizing saidamplifier comprising means for tuning out the inductive reactance' in aconnection between said circuits and an electrode of said device, meansfor reducing voltages of frequencies difierent than the frequency ofoperation of said circuits including a damping resistance in saidconnection and a circuit series tuned to the frequency of operation ofsaid input and output circuits connected in shunt to said dampingresistance.

4. A system as recited in claim 3 wherein said series tuned circuit inshunt to said damping resistance comprises a condenser and inductance.

5. A system as recited in claim 3 wherein the cathode of said device isconnected to said circuits by a circuit series tuned to the frequency ofoperation of said circuit and wherein said last named series tunedcircuit is coupled to the circuit in shunt to said damping resistance.

6. In a high frequency amplifier, an electron discharge device havinginput and output electrodes including a cathode, high frequency inputand output circuits connected with the input and output electrodes insaid device respectively, a neutralizing circuit connected between saidinput and output electrodes, a portion of said neutralizing circuitconnection being common to the connection of said input circuit to saidinput electrodes, means for stabilizing the operation of said amplifiercomprising capacitive means in said common portion of said connectionsfor tuning out the inductive reactance in said connections, means forreducing voltages of all frequencies different than the frequency ofoperation of said input and output circuits including a dampingresistance in said common portion of said connections and a circuitseries tuned to the frequency of operation of said input and outputcircuits connected in shunt to said damping resistance.

7. A system as recited in claim 6 wherein said series tuned circuit inshunt to said damping resistance comprises a condenser and inductance.

8. In a high frequency amplifier, an electron discharge device having aninput electrode, an output electrode, and a cathode, high frequencyinput and output circuits connected with the input and output electrodesin said device respectively, a circuit series tuned to the frequency ofoperation of said input and output circuits in a connection between saidcathode and said input and output circuits, a neutralizing circuitconnected between said input and output electrodes, a portion of saidneutralizing circuit connection being common to the connection of saidinput circuit to said input electrode, means for stabilizing theoperation of said amplifier comprising capacitive means in said commonportion of said connections for tuning out the inductive reactance insaid connections, means for reducing voltages of all frequenciesdifferent than the frequency of operation of said input and outputcircuits including a damping resistance in said common portion of saidconnections and a circuit series tuned to the frequency of operation ofsaid input and output circuits connected in shunt to said dampingresistance, and a coupling between said series tuned circuit in shunt tosaid damping resistance, and said series tuned circuit in saidconnection between the cathode of said tube and said input and outputcircuits.

KLAAS POSTHUMUS.

